In a conventional throttle apparatus, an air path is formed in a throttle body and a valve member adjusts the opening angle of the air path. The valve is driven by electric driving means, such as a motor, such that even when the motor stops due to a breakdown or the like, the valve member is set to a desired open position, such as slightly open to maintain an opening angle in the air path. For example, by providing a return spring that urges the valve member closed, the valve member is set slightly open, even when the motor is unable to drive the valve member. Thus, the valve member is set slightly open, thereby enabling evacuation drive of a vehicle on which the throttle device is mounted.
In the conventional throttle apparatus, the throttle body and a gear housing of the motor are made of a metal material such as aluminum, manufactured with high precision. The rotary shaft of speed reducing gears such as the throttle gear and motor gear are supported by the gear housing.
In recent years, however, because of a demand for reduction in weight and cost of throttle devices, the throttle body is molded from a resin. When the throttle body is made of resin, the gear housing is also made of resin. Accordingly, the gear housing and the throttle body are integrally formed. However, when this is done, the molding may distort in the throttle body and dimensional accuracy between rotary shafts of speed reducing gears largely deteriorates due to insufficient rigidity of the throttle body as compared with one made of metal.
When the dimensional accuracy between the rotary shafts of the speed reducing gears deteriorates, the gear teeth of the gears wear during use, thereby causing motor torque loss. Moreover, it becomes difficult to transmit the motor driving force to the valve member. Further, when the dimensional accuracy between the rotary shafts of the speed reducing gears largely deteriorates, the speed reducing gears are locked and the valve member cannot be driven.